Transmitter



Dec. 12, 1933.

F. c. LUNNON 1,938,631

TRANSMITTER Filed March 6, 1931 mm mm ll w INVENTOR FREDERICK CHARLEJS LUNNON,

BY N'g ATTORNEY Patented Dec. 12, 1933 UNITED STATES TRAN SBIITTER Frederick Charles'Lunnon, Chelmsiord, England, assignor to Radio Corporation of America, a corporation of Delaware Application March 6, 1931, Serial Nb. 520,587,

and in Great Britain March 20, 1930 Claims. (01. 259-717 This invention relates to keying arrangements for use in high frequency circuits. More particularly the invention relates to keying arrangements of the so-called absorber type, i.e. to ar- 6 rangements in which a transmitter, which is keyed, is kept under load during spacing periods by means of one or more thermionic tubes which are arranged to provide a load upon the source of anode potential when the transmitter is set to spacing.

According to this invention so-called absorber keying is effected by utilizing as an absorber tube during spacing periods a tube which during marking periods functions as an amplifier.

The invention is illustrated in the diagrammatic drawing accompanying the specification which shows an arrangement of oscillator and three stage cascade amplifier, in accordance with the present invention. a

Referring to this drawing, 0 represents an oscillator tube whose output circuit includes the usual fundamental oscillating circuit and is coupled through the customary coupling condenser to a first amplifier tube V1. The coupling condenser is indicated at k1. The grid circuit of the tube V1 contains a resistance R1 in series with a blocking condenser Blcl'. The output circuit of the tube V1 contains the usual neutralized tuned circuit and is coupled to a second amplifier tube V2 which is in turn coupled to a third amplifier tube V3. As will be seen the circuit arrangement of the tubes V1, V2, V3 is similar, like parts being indicated in the drawing by like reference numerals provided with suflixes appropriate to the number of the stage concerned. At B is connected a source of anode potential which is common to all the tubes. X1, X2 and X3 represent series resistances which may, if desired, be provided for reducing the amplitudes of the potentials applied from the source B to the anodes of the earlier stages. It is, of course, not necessary that there be a common anode source nor is the provision of resistances X1, X2, X3 an essential.

The negative terminal of-the source of anode potential is connected through a resistance Z to the common cathode connection and a key K shunted by a 'co'ndenser'as shown is connected across the said resistance Z. The grid. circuits of the amplifier tubes are completed as shown to tapping points P1, P2 and P3. The adjacent terminals of the devices R1 and 3701, R2. and Bk2, R3 and Bk3 are connected to the points P1, P2 and P3 respectively of the resistance-Z. It will be observed that the grid circuit of the oscillator 0 contains a resistance R0 and a capacity BkO arranged in similar'manner to the corresponding parts of the amplifiers, the grid circuit of the said oscillator being connected to a tapping point P0 on resistance Z.

It will be seen that when the key K is open the anode currents of the stages will fiow through the resistance Z and the various grids will therefore be biased negatively by virtue of the voltage drop in the said resistance Z, the amounts of negative bias depending on the current fiow, the value of Z, and the positions of the various tapping points. The arrangement may be such that when the key is open the negative bias applied to the grid of the oscillator 0 is sufiicient to stop oscillations with the result that the driving voltage is removed from the grids of all the subsequent stages. Preferably the arrangement is such that when the key is open the negative bias applied to the grid of one of the intermediate stages is suflicient to reduce the input of that stage to zero thus removing the driving voltage from subsequent stages, whilst leaving the master oscillator and the previous stages (if any) functioning. It will be observed however thatin both stage arrangements anode current continues to flow in the stages subsequent to that at which the negative grid bias is applied and the power represented by this current at the effective anode potential is of course dissipated in the tubes in question.

The amount of this dead loss anode current in each stage is controlled by the negative grid bias derived from the resistance Z which is in turn determined by the value of the said resistance and the position of the appropriate tapping points. For best results these variables should be so adjusted that the power dissipated in the tubes of each stage is as great as can be permitted. In general the power which may be allowed 95 to be taken by each stage when the key is open will be about 25% of thattaken when the key is closed. The output from the source of anode potential B will therefore alternate during keying from full load to about 25% of full load. It will therefore be observed that during keying there is no discontinuity or interruption from the source B so that the transit time of the key need not be considered. This feature will-be found of particular advantage when the source of potential B is constituted by a direct currentgenerator or by rectified and smoothed alternating current and in such cases greatlyimproved voltage regulation and increased factor of safety will result ascompared with most known methods of key- 1170 potential.

ing. A substantial advantage of the invention lies in the fact that the only additional apparatus required for effecting absorber keying is the resistance Z and (of course) the key.

In cases in which a plurality of sources of anode potential is employed the negative terminals of all the sources shall be connected together and then through the common resistance Z to the common cathode connection.

A method of predetermining the value of the resistance Z so that the valve in each stage subsequent to the one that is cut off will set itself at that point in its characteristicat which'it dis sipates as absorber its maximum permissible anode loss will be understood from the following example. Consider the case in which the.'oscillator stage 0 is that which is to be out Oh when the key is opened, i. e. the driving voltage is to be'r'emoved from the grids of the subsequent stages Vl, V2, V3. Letthe permissible anode loss in the stage V1, V2, V3 be respectively 111, v2, 123 watts. lithe anode potential'be VBthen for the stage V1 the current whichcan be allowed to flow during spacing periods is Q. VB Similarly with tubes V2, V3 the permissible current will be and v3 VB Thus when the key is open the total current through the resistance Z will be Let 121g, 172g, 123p be the negative bias potentials required to'settubes V1, V2; V3 respectively at the points on their characteristics at which the plate current at no signal and at anode potential V will be respectively. Suppose the potential vlgbe the greatest of these three values of negative bias Then the value of Z required is v1+v2+v3 and the grid of the first amplifier stage should be connected to the negative end of the resistance Z. The grids of the two subsequent stages should be tappedon to Z at points such that the ratio of the resistance between the tapping point in questionand the common cathode connection to the whole resistance will be in the case of the second amplifier ie 8 and in the case of the third amplifier.

vlg

The grid of the master oscillator should be tapped on to the resistance Z at such a point that the negative potential between that point and the common cathode connection when the amplicoupled to said oscillator, an impedance included in'a portion'of a circuit which is common to the anode circuits of said oscillator and said amplifiers, means for deriving bias potential for said oscillator and said amplifiers from voltage drop occurring in said impedance and keying means in shunt with said impedance, the v impedance being such thatin one position of the keying means the bias applied to'the oscillator is sufficient to stop oscillation so that the driving voltage is removed from the input electrodes of 2. Signaling means comprising a thermionic oscillator, aplurality of thermionic amplifiers coupled in cascade and to said oscillator, an imioo pedance included in a portion of V a circuit which is common to the anode circuits of said oscillator and said amplifiers, means for deriving bias potential for said oscillator and said amplifiers from voltage drop occurring in said impedance, and keying means in shunt with said impedance, the impedance being of such a value that in one position of the keying means the bias applied to one ofv the initial amplifiers coupled to said oscillator is brought to avalue to render said amplifier inoperative whereby driving voltage is removed from subsequent amplifiers. 7

3 A signaling arrangementcomprising atherrnionic tube oscillator, a plurality of cascade connected thermioniotube amplifiers coupled to said oscillator, anode circuits for said oscillator and amplifiers, said anode circuits having a common portion, a resistance included in said com- ,mon portion, connections tapped to said resistance, said connections being connected to the lator and amplifiers, and a key in parallel with said resistance.

4. A transmitter arrangement comprising an oscillation generator including, a thermionic. .tube, a plurality of thermionic tubes connected therewith, energizing circuits connected between the output electrodes of the tube in said oscillation generator and the output electrodes of each of said second mentioned tubes, said energizing circuits having a portion in common, an impedance common to said energizing circuits, a key connected in shunt to said impedance, and connections between the control electrodes of said tubes and points on said impedance, such as to cause'said oscillator. to develop oscillations and said tubes to act as amplifiers of the oscillations generated by said generator when said key is closed and to bias said oscillator to cut-off while permitting said amplifiers to draw a predetermined amount of energy from said source when said key is open.

5. A circuit, forimproving the power regulation of signalling devices comprising, a plurality oi-relaying tubes ofthe termionic type connected in cascade and adapted to supply oscilgrid electrodes of said oscillator and said amplifiers to apply bias to the grids of said oscillating energy to a load circuit, the intensity of which energy is modulated at signal frequency comprising, direct current energizing circuits connected between the output electrodes of said tubes, said circuits having a portion in common,

an impedance in said common portion, modulating means connected with said impedance for varying or modulating the amount of energy flowing in said impedance at signal frequency, thereby varying the amount of oscillating en- 

